MOBPHOLOGY AND EVOLUTION
In many species the branches of the aortic arch are as in Man. Thus the arch gives off the left subclavian, left common carotid, and innominate arteries, the latter breaking up into the right subclavian and right common carotid arteries. The heart is more vertical than in the Anthropoid Apes and an azygos lobe of the right lung
lies below it.
Respiratory and Vocal Organs.—No trace of air sacs communicating with the laryngeal ventricles exists, but other diverticula are present in some species. In Midas rosalia, according to Cnvier, a pouch communicates with the laryngeal cavity between the thyroid and cricoid cartilages; in AteJes paniscus there is a large membranous sac behind the cricoid cartilage; and in Alouatta the hyoid bone is expanded and ballooned to form a resonating chamber, which is protected by the extensive mandibular rami. The left lung has two or three lobes, and the right one has four, of which one is
the azygos lobe.
Urogenital Organs.—The kidneys have many papillae in Aides, but one papilla only is present in each kidney in all other genera. And Ateles agrees with Man and the Chimpanzee in retaining the primitive condition of several papillae.
The penis terminates in a glans of variable shape. In Cebus there is an os penis, but that structure is absent in Ateles and Lagothrix. A scrottun is present, but the communication with the abdominal cavity frequently remains open.
The clitoris varies in size, and reaches large proportions in Ateles; so that it may sometimes be mistaken for a penis. An os clitoridis may be present. The urethra does not traverse the clitoris.